This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/CH01/00072 which has an International filing date of Jan. 31, 2001, which designated the United States of America.
1. Technical Field
The invention relates to a radiation guide switch arrangement as claimed in the precharacterizing clause of patent claim 1, and to a method for producing it as claimed in the precharacterizing clause of patent claim 10.
2. Prior Art
A radiation guide arrangement is known from WO 98/12589. The known arrangement has four optical fiber insert channels, which run toward one another in the form of a star, with optical fibers inserted in them. A moveable switching part was arranged at the intersection point of the projection of the fiber ends. The switching part could be withdrawn from the intersection point, as a result of which it was then possible for light to be transmitted between any two opposite optical fiber ends. This light transmission was inhibited when the switching part was inserted. Since the switching part was mirrored, light transmission then occurred via the mirror surface between two adjacent fiber ends arranged at 90xc2x0 to one another.
The switching part was arranged in a holder which was in the form of filigree and had two pairs of leaf springs arranged one behind the other on the left and right. The longitudinal faces of each leaf spring had a first comb structure, which engaged in a second comb structure that was arranged in a fixed position on a base plate. The comb structures could be attracted to one another or repelled from one another by applying an electrical voltage, by which means the switching part was drawn in or drawn out at the intersection point. A mechanical stop was provided on the leaf springs for each defined position of the switching part.
The object of the invention is to provide a radiation guide switching arrangement which has low radiation losses, or exactly adjustable radiation losses, with a good switching response.
The object is achieved by producing a radiation guide arrangement having at least one radiation guide switch from a sandwich wafer with a substrate, a covering layer, and an electrically insulating intermediate layer. Each radiation guide switch has at least one moveable switching part as well as at least two radiation guide ends which come to rest in a plane. The radiation guide ends are arranged closely adjacent to one another such that radiation which emerges from one radiation guide end can be blocked on its optical path to another guide end, or can be reflected into this other guide end, by means of the switching part. The intermediate space which holds the switching part is, according to the invention, filled with an index matching liquid having a predetermined refractive index. Furthermore, the core of each radiation guide, which carries the radiation, is designed to taper such that radiation collimation can be achieved by interaction with the refractive index of the index matching liquid and the free core profile in the space which is filled with liquid.
It is thus not sufficient to arrange the radiation guide ends as close to one another as possible. The end region of each radiation guide and the refractive index of an index matching liquid between the radiation guide ends should be matched to one another so as to ensure good radiation transmission between the radiation guide ends. In order to achieve good radiation transmission, the guide ends are designed, and the corresponding index matching liquid is chosen, such that the radiation which emerges from one guide end is passed to the other guide end with only low losses. Radiation guidance with losses that are as low as possible can be achieved in the free space (which is filled with index matching liquid) between the ends if the beam which emerges from the guide end can be passed to the other guide end with the same beam diameter. This means that a collimated beam must emerge from the guide end. Radiation collimation is achieved by designing the guide core which carries the radiation such that it tapers in its end region, and by searching for the index matching liquid such that its refractive index for the radiation which is to be transmitted in the radiation guide results, together with the core profile, in the desired lens effect for radiation collimation.
The refractive index of the index matching liquid should at most be of equal magnitude to refractive index of each radiation guide core. The refractive index of the liquid is preferably chosen to be between 99.90% and 98.00% with respect to the core refractive index. Very good results can be achieved with a refractive index between 99.4% and 98.6%. If the distance between the guide ends is short (in the region of 30xcexcm), a good value of the refractive index is obtained in the region of 99.1% (at 25xc2x0 C.). This value allows stable coupling at a temperature range between xe2x88x9210xc2x0 C. and 85xc2x0 C. at a wavelength of between 1250 nm and 1630 nm. This value should increase if the distance is greater.
The radiation guide switching arrangement according to the invention also makes use of radiation guide switches with a mirrored switching part. If a switching part such as this is used, then, on the one hand, it is possible to xe2x80x9cpass on radiationxe2x80x9d between mutually opposite radiation guide ends when the switching part is withdrawn from the intermediate space, as already indicated above. When the switching part is inserted into the intermediate space, the passing on of radiation is interrupted; however, radiation which emerges from a radiation guide can now be reflected (passed on) into another radiation guide. If passed on xe2x80x9cstraightxe2x80x9d, the collimated beam emerges from the one guide and enters the opposite guide. If not, the collimated beam is deflected by the mirror. In order that this switching operation can operate with minimal radiation losses, the radiation guide ends as well as the mirrored surface must be positioned exactly. To do this, all the radiation guide ends to be switched are located in a plane. The mirror surfaces of the switching part must then be positioned at right angles on this plane. It has now been shown that a mirrored switching part which was produced according to the method described in WO98/12589 had mirror surfaces which are not at right angles, which then led to additional radiation losses between two guide ends.
It has now been found that those surfaces of the switching part from WO98/12589 which are not at right angles were a result of the etching process described there. In contrast to WO98/12589, a sacrificial web is now in each case produced at a short distance in front of the mirror surfaces which are to be produced by etching. This greatly reduces any space holding etching ions in front of the mirror surfaces to be produced, thus making it possible to prevent, or greatly minimize, oblique etching. Mirror surfaces produced in this way are now at right angles.
The expression a good switching response does not just mean that the radiation is transmitted with losses that are as low as possible when the switch is in the xe2x80x9cswitched-on positionxe2x80x9d. The switching times must also be reproducible, and it must be possible to carry out the switching operations quickly. However, this also refers to switching processes by means of which a predetermined attenuation can be set. However, the switching times in the case of the radiation guide switch known from WO98/12589 differed; furthermore, high voltages had to be applied to the comb structure of each holder having a switching part, in order that it was possible to overcome the xe2x80x9ctearing free effectxe2x80x9d from one switching position to the other.
It has been possible to eliminate this xe2x80x9ctearing free effectxe2x80x9d in the embodiment described below since two identical comb structure engaging in one another have no longer been used, and, instead the tine end region of one of the two comb structures has a region with a broadened cross section. This thus results in a second fixed-position comb structure which matches the first comb structure. The comb tines of the second comb structure are arranged with a gap with respect to the first comb structure. A first and a second electrical voltage can be applied to the two comb structures in order to produce an electrostatic movement. It is now possible to configure the region with a broadened cross section, that is to say to design it with an electrostatic voltage application, such that the switching part can be held in a stable position.
At least one leaf spring element is firmly connected to the holder. The leaf spring elements are designed such that they run approximately at right angles to the movement direction of the holder.
In addition, it has been shown that this configuration, which will be described in more detail in the following text, made it possible for the index matching liquid to be displaced out of the intermediate spaces between the tines easily. This resulted in a faster switching response than the switch in WO98/12589.
The electrostatic force between adjacent tines in the first and second comb structures depends on the width of the gap between these tines. With a conical, arrow-shaped tine configuration, the gap width varies to a greater extent with the mutual separation between the two structures than in the case of tines of the same thickness, as in WO98/12589. For this reason, there was no need for the movement stops as in WO928/12589; surprisingly, there is now no longer any tearing free effect.
The switching part may also be designed without being mirrored. It can then be inserted into a radiation-carrying space in the intermediate space between two respective guide ends so as to achieve a predetermined radiation attenuation. The attenuating part of the switching part, which can be inserted into the radiation-carrying space, is preferably provided with a metal coating. Furthermore and in particular, the attenuating region of the switching part is no longer arranged at right angles to the aligned axis of the two guide ends, but at an angle xcex1 of less than 65xc2x0 and preferably of less than 50xc2x0. This makes it possible to reduce polarization-dependent attenuation resulting from the inserted attenuating part.
Instead of having to operate with just one switching part as stated above, a number of switching parts may be used in a single radiation guide switch. Each switching part can then be moved in front of in each case two radiation guide ends of two radiation guides such that radiation coupling and attenuation respectively is possible. The switching parts are preferably associated with the radiation guide ends such that output radiation from a number of radiation guide ends can in each case be coupled individually into a single radiation guide end, depending on the switching position of one of the switching parts. Furthermore, the arrangement may optionally be designed such that the output radiation from a single radiation guide end can in each case be coupled individually into one of the other radiation guide ends, depending on the switching position of one of the switching parts.
A fluid-tight housing with fluid-tight bushings for the radiation guides and the electrical cables is preferably provided. The interior of the housing is then filled with the index matching liquid, except for a gas bubble. The volume of the gas bubble is predetermined such that any pressure in the interior of the housing resulting from thermal effects is not greater than or less than a predetermined value.
Instead of producing a single radiation guide switching arrangement, a number of switches can be produced which are arranged like a matrix in one plane, preferably on a first chip. In particular, this chip has integrated electrical guide subelements for electrical voltages which can be applied to the switches. A second chip, which is in the form of a waveconductor chip and is preferably applied using flip chip technology, is then provided for the optical and, preferably, the electrical connections between the switches.
The radiation guide switching arrangement having at least one radiation guide switch, which has one switching part, is produced from a sandwich wafer. The sandwich wafer has a substrate, a covering layer and an electrically insulating intermediate layer. As has already been stated above, the switching part can be moved in front of at least two radiation guide ends which lie in a plane. The radiation guide switching arrangement, inter alia with the switching part and the guide channels for the radiation guides and their ends, is produced by means of an etching process from the sandwich wafer. The etching process is used to produce at least one sacrificial web in the immediate vicinity of each of the outer faces of the switching part, which run at right angles to the plane, in order to avoid the outer faces having a profile which differs from the normal to the plane.
The sandwich wafer has a covering layer which is composed essentially of silicon and whose unmasked areas are removed in an ion etching process. Each sacrificial web is at a distance of approximately 10 xcexcm, with a distance tolerance of xe2x88x925 xcexcm to +20 xcexcm, for a covering layer thickness of approximately 73 xcexcm with a thickness tolerance of xc2x13 xcexcm.